1. Field of the Invention
The present invention relates to an image forming apparatus, an image forming system and a lubricant amount control method.
2. Description of Related Art
In an image forming apparatus using an electrophotographic scheme, a cleaning device of a blade-cleaning type is known in which a plate-shaped cleaning blade composed of an elastic body and serving as a device for removing remaining toner such as untransferred toner and transfer residual toner on an image bearing member is brought into contact with the surface of the image bearing member to thereby remove the remaining toner on the image bearing member, for example.
In recent years, in image forming apparatuses using an electrophotographic scheme, reduction of toner particle size has been in demand from the view point of enhancing the image quality, and for such a purpose, polymerization methods such as an emulsion polymerization method and a suspension polymerization method have been utilized, for example. As the size of the toner particle decreases, however, the attaching force between the toner particle and the image bearing member increases, thus reducing the ease of removal of the remaining toner on the image bearing member. In particular, when so-called polymerization toner produced by a polymerization method is used, the toner particles have a substantially spherical shape, and as a result cleaning defects in which the toner particles roll on the image bearing member and slip through the cleaning blade are easily caused, thus further reducing the ease of removal of the remaining toner on the image bearing member. Furthermore, when toner slips through the cleaning blade, toner aggregate formed on the image bearing member is formed centered on the toner as the core, and grain blank slipping (grain noise) is generated on the solid image printing part.
To solve such a quality problem as the above-mentioned “slipping” and “grain noise” today, lubricant-external additive (lubricant) is supplied onto the image bearing member to perform cleaning in the state where the attaching force between the toner particle and the image bearing member is suppressed to a low level. Examples of the method for supplying lubricant onto the image bearing member include a lubricant application process in which lubricant is scraped by a brush and supplied to the surface of the image bearing member, a toner adding process in which a toner image is formed with use of lubricant-containing toner to supply the lubricant.
In the toner adding process, the lubricant exists in the developing section in a state in which the lubricant is adhered to or free from the toner, and when the toner is supplied to the image bearing member in the image section, the lubricant is also supplied onto the image bearing member. Since the lubricant is charged to a polarity opposite to that of the toner, the lubricant is also supplied onto the image bearing member in the background section. When images with a low area ratio are successively formed, lubricant is consumed in the background section, but there are fewer image sections and toner in the developing section is not consumed, and therefore new toner is not supplied into the developing section. The lubricant is supplied by the toner into the developing section, and so if this condition continues, the amount of lubricant in the developing section decreases.
When the amount of lubricant in the developing section decreases, there may be regions where the amount of lubricant supplied to the surface of the image bearing member decreases or regions where no lubricant exists, and it may be impossible to decrease the amount of lubricant attached to the toner—the purpose of supplying the lubricant to the image bearing member, which is more likely to cause problems such as slipping and grain noise.
In order to prevent the above-described problems, a patch image (toner image) is formed in a region other than the image region on the image bearing member when an image with a low area ratio is formed. With the formation of the patch image, the lubricant is supplied onto the image bearing member, and when the toner in the developing section is consumed, new toner is replenished into the developing section. When new toner is replenished, the lubricant is also replenished, thus preventing reduction of the amount of lubricant in the developing section and, by extension, preventing reduction in the amount of lubricant on the image bearing member as well.
The lubricant in the developing section may be supplied onto the image bearing member by forming the patch image with a certain margin based on the area ratio of images, but in that case, a patch image may be formed inadvertently even when the amount of lubricant in the developing section is appropriate. Since the toner used for the patch image is disposed without being processed, forming many patch images results in high printing cost.
When images with a high area ratio are successively formed, the new toner and the lubricant added in the toner are supplied into the developing section and the lubricant on the image bearing member is also collected from the image bearing member into the developing section, and so the amount of lubricant in the developing section increases. However, an excess of the amount of lubricant in the developing section may result in a reduction of the amount of charging of toner, causing problems such as fog toner into the background section and image quality degradation. Furthermore, when the amount of lubricant in the developing section increases, the amount of lubricant supplied onto the image bearing member also increases, causing the torque between the image bearing member and the cleaning blade to increase, resulting in a problem that turn-up of the blade or abrasion increases.
As described above, the amount of lubricant in the developing section and the amount of lubricant on the image bearing member have their respective appropriate ranges.
On the other hand, in the lubricant application process, lubricant is supplied onto the image bearing member by an application device such as a brush, but the lubricant on the image bearing member is collected into the developing section in the development region as in the case of the toner adding process. An increase in the amount of lubricant in the developing section may cause problems such as the occurrence of fog toner or image quality degradation. Conventionally, control is performed to eject the lubricant in the developing section onto the image bearing member in order to prevent an increase of the amount of lubricant in the developing section. Moreover, when lubricant is collected into the developing section and the amount of lubricant on the image bearing member decreases, problems such as slipping or grain noise occur as in the case of the toner adding process.
To solve the above-described problems, Japanese Patent Application Laid-Open No. 2014-142472 and Japanese Patent Application Laid-Open No. 2014-145864 disclose a configuration in which the amount of lubricant on an image bearing member is controlled based on an image area ratio of the surface of the image bearing member.
Japanese Patent Application Laid-Open No. 2014-142472 discloses a configuration in which the surface of a photoconductor drum is divided into a plurality of regions in a direction crossing the rotating direction and a supply of lubricant is controlled region by region.
Japanese Patent Application Laid-Open No. 2014-145864 discloses a configuration in which a patch image between images is formed based on gradation information of the images and lubricant is selectively supplied to a region where a cleaning defect is likely to occur.
However, since the amount of lubricant in the developing section varies depending on differences in an environment and the degree of toner degradation, even the configurations described in the above literature may be subject to problems such as slipping, grain noise or fog toner.